Biochemical effects of mild iron deficiency and cold acclimatization on rat skeletal muscle

Most of the previous studies on the effects of iron deficiency on skeletal muscle respiratory capacity and work performance have been investigated in severe or moderate iron-deficiency anemia. We report here that even in mild iron deficiency where the hemoglobin concentration was 10 g/dl and the iron stores in livers and spleen were not completely depleted, a marked reduction in succinate dehydrogenase was observed in skeletal muscles but not in heart. Similarly, cytochrome oxidase activities were reduced. Although no significant change in glycerophosphate dehydrogenase was detected in the iron-deficient rats, exposure to cold in this group greatly reduced this enzyme activity. As cold acclimatization accelerates marrow erythropoiesis (20) which in turn, demands more iron, it seems that in the iron-insufficient state, this iron demand for marrow activity may persist at the expense of the tissue iron pool, resulting in a marked reduction in glycerophosphate dehydrogenase activities. Since succinate dehydrogenase plays a significant role in the impairment of mitochondrial function and early fatigue of iron-deficient muscle (11), the present study shows that even in mild iron deficiency, some loss of muscle functions could result as succinate dehydrogenase activities were greatly reduced.     

Neural inhibition sharpens auditory spatial selectivity of bat inferior collicular neurons

This study examines the role of neural inhibition in auditory spatial selectivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, using a two-tone inhibition paradigm. Two-tone inhibition decreases auditory spatial response areas but increases the slopes of directional sensitivity curves of inferior collicular neurons. Inferior collicular neurons have either directionally-selective or hemifield directional sensitivity curves. A directionally-selective curve always has a peak which is at least 50% larger than the minimum. A hemifield directional sensitivity curve rises from an ipsilateral angle by more than 50% and either reaches a plateau or declines by less than 50% over a range of contralateral angles. Two-tone inhibition does not change directionally-selective curves but changes most hemifield directional sensitivity curves into directionally-selective curves. Auditory spatial selectivity determined both with and without two-tone inhibition increases with increasing best-excitatory frequency. Sharpening of auditory spatial selectivity by two-tone inhibition is larger for neurons with smaller differences between excitatory and inhibitory best frequencies. The effect of two-tone inhibition on auditory spatial selectivity increases with increasing inhibitory tone intensity but decreases with increasing intertone interval. The implications of these findings in bat echolocation are discussed. Accepted: 18 January 2000     

Differences between Indica and Japonica rice varieties in CO2 exchange rates in response to leaf nitrogen and temperature

Four Indica and five Japonica varieties of rice (Oryza sativa L.) were examined to elucidate their differences in photosynthetic activity and dark respiratory rate as influenced by leaf nitrogen levels and temperatures. The photosynthetic rates of single leaf showed correlations with total nitrogen and soluble protein contents in the leaves. Respiratory rate was also positively correlated with the leaf nitrogen content. When compared at the same level of leaf nitrogen or soluble protein content, the four Indica varieties and one of Japonica varieties, Tainung 67, which have some Indica genes derived from one of its parents, showed higher photosynthetic rates than the remaining four Japonica varieties. At the same photosynthetic rate, the Indica varieties showed lower respiratory rate than Japonica varieties. When the leaf temperature rose from 20°C to 30°C, the photosynthetic rate increased by 18 to 41%, whereas the respiratory rate increased by 100 to 150%. These increasing rates in response to temperature were higher in the Japonica than in the Indica varieties. In this respect, Tainung 67 showed the same behavior as of the other four Japonica varieties.Abbreviations 30/20 ratios the ratios of photosynthetic and respiratory rates at 30°C to those at 20°C     

Opioid-binding protein (OBCAM) is rich in β-sheets

Based on circular dichroism (CD) and the sequence-predictive method, the opioid-binding cell adhesion molecule (OBCAM) consisted of one half -sheets and one fourth -helices. This is consistent with significant sequence homology of the protein to several members of the immunoglobulin (Ig) superfamily, particularly cell adhesion molecules, which are rich in -sheets. Hydropathy analysis suggests that hydrophobic and hydrophilic regions were evenly distributed along the sequence, but the NH₂- and COOH-termini were hydrophobic. Hydrophobic moments and Fourier-transform amphipathic analyses further suggest that residues 23–30 and 83–93 were amphiphathie -sheets. The overall conformation of OBCAM was unaltered by adding linoleic acid, which is required for opioid ligand binding.     

Two different sites of action for platelet activating factor and 1-O-alkyl-2-O-methyl-sn-glycero-3-phosphocholine on platelets and leukemic cells.

2-O-Methyl analogs of platelet activating factor (PAF) are potent anticancer agents. The sites of action and mechanisms of cell toxicity of these agents are as yet unknown. To better understand the mode of action of this class of anticancer agents, we examined the ability of 1-O-hexadecyl-2-acetylglycero-3-phosphocholine with the S or R configuration at C2 ((R)-PAF and (S)-PAF) and 1-O-hexadecyl-2-methoxyglycero-3-phosphocholine with the S or R configuration at C2 ((R)-ET-16-OCH3-GPC and (S)-ET-16-OCH3-GPC) to induce rabbit platelet aggregation and to inhibit [3H]thymidine uptake into WEHI-3B cells, HL-60 cells, and normal blood lymphocytes. The four chiral ether-linked lipids caused aggregation of rabbit platelets with the following order of potency: (R)-PAF greater than (S)-PAF greater than (R)-ET-16-OCH3-GPC greater than (S)-ET-16-OCH3-GPC; the EC50 values were 1 pM, 50 nM, 1 microM, and 50 microM, respectively. The cytotoxic effects of these ether lipids in leukemic cells was in reverse order to that observed for aggregation of platelets. The order of potency for inhibition of [3H]thymidine uptake by WEHI-3B and HL-60 cells was (R)-ET-16-OCH3-GPC = (S)-ET-16-OCH3-GPC greater than (S)-PAF greater than (R)-PAF; the EC50 values were 2, 2, 15, and greater than 40 microM, respectively. PAF antagonists (WEB 2086, CV 3988, triazolam, and SRI 63,441) blocked the action of the four ether lipids on platelets, while SRI 63,441 blocked the antineoplastic activity of the ether lipids on WEHI-3B and HL-60 cells. None of the four lipids was able to kill normal lymphocytes significantly. Scatchard analysis of PAF receptor binding revealed that HL-60 and WEHI-3B cells, which are sensitive to the cytotoxic action of ether-linked lipids, do not possess PAF receptors, whereas both normal lymphocytes and platelets do possess a PAF receptor. The present data indicate that the cytotoxic action of antineoplastic ether-linked lipids does not involve the PAF receptor. The protective role of SRI 63,441 in blocking the proaggregatory activity of the ether lipids in rabbit platelets involves PAF receptor, but cytotoxic activity against WEHI-3B and HL-60 cells does not result from its ability to act as a PAF antagonist.     

The inhibitory effects of some adenosine analogues on transmitter release at the mammalian neuromuscular junction

An electrophysiological study was made of the effects of four adenosine analogues, 2-chloroadenosine (2-CIA), 5'-N-ethylcarboxamidoadenosine (NECA), L-N6-phenylisopropyladenosine (L-PIA), and 2-(p-methoxyphenyl)-adenosine (CV-1674) on neurotransmitter release in the mouse phrenic nerve - hemidiaphragm preparation. All four drugs decreased miniature end-plate potential frequency in a dose-dependent manner. Evoked transmitter release in the cut diaphragm preparation was depressed by 2-CIA and CV-1674 to a similar extent. The ability of theophylline to antagonize the inhibitory effect of CV-1674 on spontaneous transmitter release was also established. On the basis of these results, the rank order of potencies was: L-PIA greater than NECA greater than 2-CIA greater than CV-1674. A clear classification of receptor type could not be made, since the ratio of potencies of L-PIA and NECA was narrow. Different slopes of the concentration-effect curves for 2-CIA and CV-1674 compared with L-PIA and NECA suggest an additional component to simple agonist action in their overall effects.     

Cloning and nucleotide sequence of the tzs gene from Agrobacterium tumefaciens strain T37.

The trans-zeatin secretion locus (tzs), from the nopaline Ti plasmid of Agrobacterium tumefaciens strain T37, was cloned and the nucleotide sequence determined. This gene is located in the virulence region of pTiT37. The tzs gene is responsible for the secretion of trans-zeatin into bacterial culture medium and in addition has the cytokinin biosynthetic activity, dimethylallylpyrophosphate:AMP dimethylallyltransferase. Sequence analysis showed an open reading frame of 729 nucleotides, capable of encoding a protein of 27,545 daltons. A single new labelled protein of 27,200 daltons was detected in Escherichia coli maxicells expressing the cloned tzs gene. Significant sequence homology was observed between the tzs and the published tmr sequence from pTiT37.     

Phospholipid-Sensitive Ca2+-Dependent Protein Kinase Preferentially Phosphorylates Serine-115 of Bovine Myelin Basic Protein

Phospholipid-sensitive Ca2+ -dependent protein kinase (PL-Ca-PK) and cyclic AMP-dependent protein kinase (A-PK) both preferentially phosphorylated serine residues of bovine myelin basic protein (MBP). Tryptic peptide maps of MBP phosphorylated by PL-Ca-PK or A-PK, however, revealed different phosphopeptides, suggesting a difference in the intramolecular substrate specificity for the two enzymes. Serine-115 of MBP, in the sequence (-Arg-Phe-Ser(115)-Trp-), was found to be a preferred and probably major phosphorylation site for PL-Ca-PK. Because serine-115 of bovine MBP corresponds to serine-113 of rabbit MBP, an in vivo phosphorylation site reported by Martenson et al. (1983), and PL-Ca-PK is present at a very high level in brain and myelin, it is suggested that the enzyme may be responsible for the in vivo phosphorylation of this and other sites in MBP.